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Fires Threaten Mount Wilson Transmitter Sites

This past week has been a difficult one for TV and many FM radio stations in Los Angeles. As the "station fire" threatened Mount Wilson, personnel were ordered to evacuate the area. This is the first time in the 33 years I've been involved with broadcasting in Los Angeles that I can remember this happening. From a distance, engineers watched as flames threatened their transmitter sites and the historic Mount Wilson observatory.

The amazing thing is that in this harsh environment, with smoke, soot and high temperatures, I didn't hear of any station going off the air. This is a testament to the maintenance and planning of the stations' engineers and, perhaps most important, the dedication of the fire fighters working to protect the facilities.

On Wednesday, station personnel were allowed back to the site and found that the landscape at Mount Wilson had changed. Crews removed trees from around the buildings, towers and roads. Initial reports are no structural damage but dirty air filters and ventilation systems from the smoke and soot.

Larry Lopez (Angeles Crest Services) provides the key maintenance services that keep Mount Wilson running. He's posted photos and updates on the fire at and Updates.htm. Bob Gonsett provided regular updates on the Mount Wilson situation via email to CGC Communicator subscribers. If you have facilities in Southern California and are not receiving Bob's e-mails, check it out. I've found it to be the best source for almost real-time updates on critical issues affecting TV and radio broadcast engineering in Southern California.

Kerry Cozad from Dielectric recommended that stations check their antennas to make sure soot and ash has not gotten on- or into them. Exposed VHF and FM antennas are at the greatest risk, but unpressurized slot antennas could also be affected if soot and ash gets inside their radomes. Los Angeles has had low humidity during the fires, so problems may not appear until rain comes. As with any antenna problem, operators need to be reminded not to keep hitting the "reset" button if they get a VSWR (reflected power) fault. They should switch to a backup antenna, or, if that's not available, and you are willing to take the risk of burning up the antenna, reduce power significantly. If an arc has developed, continuing to put power into the line and antenna will likely result in damage to the antenna that could be difficult to repair.

Doug Lung is one of America's foremost authorities on broadcast RF technology. He has been with NBC since 1985 and is currently vice president of broadcast technology for NBC/Telemundo stations.